Spanning Tree Protocol is a link management protocol that provides path redundancy while preventing undesirable bridging loops in the network. For an Ethernet Layer-2 network to function properly, only one active path can exist between two stations. Multiple active paths between stations cause traffic to loop in the network. If a bridging loop exists in the network topology, it can cause broadcast and multicast frames to be duplicated, creating a traffic storm. When bridging loops occur, a bridge may see the same stations appearing on both of its interfaces. Additionally, switches may see the same stations appearing on different ports at different times. This condition confuses the frame forwarding logic. To provide path redundancy, Spanning Tree Protocol defines a tree that spans all devices in the Layer-2 network. Spanning-Tree Protocol forces all redundant data paths into a standby (blocked) state. If the network topology changes, or if the network Spanning Tree Protocol configuration changes, the spanning-tree algorithm reconfigures the spanning-tree topology and reestablishes the link by activating the standby path or putting active links into standby state. The IEEE 802.1D Standard, entitled “Media Access Control (MAC) Bridges,” defines a Spanning Tree Protocol for use in local area networks (LANs).
Bridges in an extended LAN participating in Spanning Tree Protocol gather information on other bridges in the network through observation and forwarding of STP messages. These STP messages are so-called bridge protocol data units (BPDUs). This results in selection of a unique root bridge for the stable spanning tree network topology and the removal of redundant path in the switched network by placing redundant switch ports in a blocked state. Spanning Tree Protocol operation is transparent to end stations, which are unaware of the network topology of the LAN segment to which they are being connected. Generally speaking, the root bridge originates configuration BPDUs, which other devices process and multicast out at STP-enabled ports.
FIG. 1 is a functional block diagram 100 illustrating example physical connections (102-112) between various network devices, such as Ethernet switches, wireless access points, and/or wireless mesh nodes (114-120). At startup of an instance of STP, the network devices (114-120) begin to exchange messages with each other via the various connections (102-112) in an effort to determine a root. Generally (and unless configured otherwise), the network device with a lowest numerical MAC address is the root. After the root has been determined, redundant paths are isolated. FIG. 2 is a diagram 200 illustrating example logical connections between various network devices wherein redundant paths and associated ports of blocked network devices are also identified. Solid lines (200, 204, 206) indicate active connections between the root R and other network devices (208-212). Conversely, dashed lines (214-218) indicate a redundant, blocked link. Generally, when a redundant link is blocked, the network device will not forward packets out, and drop incoming packets received on, the port corresponding to the blocked link. The network device on the other end of the blocked link, however, is not aware that the first network device has blocked the link, and will continue to forward multicast, broadcast and flooding unicast traffic on this link.
In a wired environment such as an Ethernet environment, there is generally plenty of Ethernet link and port bandwidth. As a result, having device 210 continue to transmit packets that will intentionally be dropped by device 208, and other similar situations between other devices, is not usually a concern. The spanning tree protocol can also be used in wireless mesh networks to configure a tree-based Layer-2 network. However, in wireless networks, this situation may not desirable, since the medium is shared, and less bandwidth is typically available on wireless networks. As a result, transmitting those superfluous packets will likely have a detrimental effect on bandwidth and available CPU power.
In light of the foregoing, a need in the art exists for methods, apparatuses and systems that allow for, or facilitate, preventing network devices from transmitting unnecessary packets over a redundant link to a blocked port. The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.